Room temperature curable hybrid silicones

ABSTRACT

A novel moisture curable polymer combination comprising, a member selected from the group consisting of a polydiolefin polymer containing olefinic unsaturation in either the main polymer backbone or in pendent side chains; and a loop polymer having a polymeric backbone and a plurality of olefinic groups which have been converted to closed loops by reaction with difunctional organic compounds reactive with said olefinic groups, said olefinic groups from which the loops are formed may either be present within the backbone and/or pendent from the polymeric backbone; and a silicon crosslinking compound containing at least one easily hydrolyzed substituent.

[0001] This patent application is a Divisional of prior U.S. patentapplication Ser. No. 09/777,067 filed Mar. 26, 2001 which is aContinuation of U.S. patent application Ser. No. 09/363,915 filed onJul. 28, 1999, now U.S. Pat. No. 6,251,993.

[0002] The work embodied in this patent was carried out under ContractsN00014-91-C-0007 and N00014-99-C-0049 (Office of Naval Research), givingthe Government rights to a royalty-free license.

BACKGROUND OF THE INVENTION

[0003] Silicones have become important commercial polymers because of acombination of properties, including high thermal stability, Noll, W.,“Chemistry and Technology of Silicones”, Academic Press, New York, N.Y.,1968, 388; low surface tension, Voronkov et al, “The Siloxane Bond”,Consultants Bureau, New York, N.Y., 1978; low glass transitiontemperature, optical transparency, Lewis, F. M. in “High Polymers”,Vol.XXIII Pt.2, Kennedy, J. P. and Tornquist, E. G. M., eds, Ch.8,Interscience, New York, N.Y., 1969; and low dielectric constant. Thesematerials, however, have relatively poor mechanical strength,Polmanteer, K. E. J. Elastoplastics, 1970,2,165 and Yilgor, I. et al,Adv. Polym. Sci. 1988, 86, 1-86; generally requiring high filler loadingto obtain acceptable properties. The poor strength is usually attributedto flaws or microcracks that grow readily because of the high mobilityof the chains, Smith, T. L., Rubber Chem. Technol. 1978,51,225.

[0004] An alternative approach to the preparation of silicones withimproved mechanical strength has been to attach difunctional silanes,such as hydride-terminated polydimethylsiloxanes, to high molecularweight polyolefins, such as polybutadiene, by hydrosilylation. Toprevent premature crosslinking and gelation, the reactions were carriedout in dilute solution. Under these conditions, after one end of apolysiloxane chain attaches to an olefin site, the other end tends toattach to a nearby olefin site on the same polybutadiene moleculeforming a silicone side-loop on a hydrocarbon backbone. The side-loopsprovide the desirable surface properties of silicones, and thehydrocarbon backbone contributes to mechanical strength. This technologyhave been described in Baum, K., U.S. Pat. No. 5,703,163; Baum, K., U.S.Pat. No. 5,811,193 and Baum, K. et al, J. Am. Chem. Soc. 1998, 120,2993-2996. This reaction is depicted in the following scheme.

[0005] Scheme 1. Side-Loop Formation.

[0006] The loop polymers have been used in the preparation of coatings.The dilute hydrolylation solution was concentrated, and the concentratewas applied to a surface. Small amounts of unreacted hydrido groups thenreacted with olefinic groups to give crosslinked coatings. However,reaction temperatures of 50-150° C. were generally required to providedesirable cure rates. While these elevated temperature conditions areacceptable for many coating applications, they are not practical forother applications, such as ship hull coatings.

[0007] This invention relates to novel room temperature curablecoatings. The room temperature curable coatings of this invention areparticularly useful as ship hull coatings.

SUMMARY OF THE INVENTION

[0008] Briefly, this invention comprises novel moisture curable polymercomposition comprising, in combination, a member selected from the groupconsisting of a polydiolefin polymer containing olefinic unsaturation ineither the main polymer backbone or in pendent side chains; and a looppolymer having a polymeric backbone and a plurality of olefinic groupswhich have been converted to closed loops by reaction with difunctionalorganic compounds reactive with said olefinic groups, said olefinicgroups from which the loops are formed may either be present within thebackbone and/or pendent from the polymeric backbone; and a siliconcross-linking compound containing at least one easily hydrolyzedsubstituent and at least one hydride substituent.

[0009] The invention further comprises exposing the above-describedcombinations of polymer and crosslinker to moisture to cross link,preferably at or around room temperature.

[0010] Still further the invention includes a substrate, usually steelor other metal, coated with the above-described combinations of polymerand cross linker, and cross linked by exposure to atmospheric moistureto form an adherent protective coating.

[0011] The polydiolefin polymers may be polybutadiene, polyisoprene,polychloroprene and the like.

[0012] The loop polymers are generally prepared by reacting apolyunsaturated material, such as polybutadiene, with a dihydridosilicon compound, such as hydride terminated polydimethyl-siloxane, inan inert solvent, such as toluene, in the presence of a hydrosilylationcatalyst. The completion of the hydrosilylation reaction can be observedby the loss of silicon hydride absorption in the infrared spectrum.

[0013] The loop polymers may also have hydroxy or carboxy groups whichcan be capped with diisocyanates or epoxies, respectively.

[0014] The polydiolefins and the loop polymers may have molecularweights on the order of 1000 or 100,000 or more.

[0015] The present invention provides coatings in which hydrolytic typecures take place at or around room temperature, although temperatures offrom about 0° F. to 100° F. are contemplated.

[0016] The cross-linking agents are silicon compounds with easilyhydrolyzed substituents, such as halogens, alkoxy groups or acyloxygroups. When coatings containing these materials are exposed to theatmosphere, atmospheric moisture causes hydrolysis, forming silanolgroups that are converted to siloxanes cross-links. Catalysts such astin compounds are frequently used.

[0017] The cross-linking according to this invention can be generalillustrated by the following reactions:

[0018] Cross linking agents contain one or more silicon atoms, with oneor more easily hydrolyzable groups on silicon, and one or more hydridofunctions on silicon. The hydrolyzable groups can be, but are notlimited to, alkoxy groups, halogens or acyloxy groups.

[0019] The cross-linking agents are typically comprise from 1 to 100mole % of the olefinic double bonds present in the polydiolefin or looppolymers.

[0020] These cross linking agents in one preferred class, can bedepicted as follows:

[0021] wherein X is a hydrolyzable group such as chloro, alkoxy oracyloxy, and Y may be either aryl, alkyl or one of said hydrolyzablegroups. The aryl and alkyl groups may be substituted or unsubstituted.Suitable substituents include halogens, alkyls, etc. The y groups can bethe same or different from each other.

[0022] The aforementioned alkoxy, acyloxy, aryl and alkyl groupstypically contain from 1 to about 20 carbon atoms.

[0023] Dimethylethoxysilane and dimethylchlorosilane are readilyavailable compounds that meet these criteria, and are preferred crosslinking agents. When loop polymers are used, the cross linking agent canbe added to the hydrosilylation mixture after the loop formation iscomplete, although the point at which it is added is not critical. Thecross linking agent adds to double bonds of the polybutadiene or otherpolydiolefin by hydrosilylation. Variation of the amount of the crosslinking agent will vary the physical properties of the finished product.

[0024] After the hydrosilylation is complete, solvent may be removed togive a material with a concentration and viscosity suitable forapplication as a coating. Optionally, other components and catalysts maybe added to vary the properties of coatings. For example, tetraethylorthosilicate may be added to increase the cross-link density, andalkoxy terminated polydimethylsiloxane, to increase toughness.

[0025] When the invention is practiced using polydiolefins, theabove-described cross linking agents, for example dimethylethoxysilane,are reacted directly with polybutadiene or other polydiolefin, omittingthe step in which a difunctional hydrosilane is used to form side-loops.

[0026] In a further preferred embodiment of the invention, when apolydiolefin without side loops is used, an additional polymericcomponent can be used. The additional polymeric component is apolysiloxane terminated with hydrolyzable groups, such as ethoxy orchloro terminated polydimethylsiloxane. The poly siloxane terminatedwith hydrolyzable groups is essentially free of Si—H groups. Theadditional polymeric compound is added before or after enough solvent isremoved to give a concentration suitable for application as a coating.After the material is applied to a substrate, co-hydrolysis of the twotypes of ethoxysilanes can give coatings with similar overallcomposition as those obtained using the side-loop method, but possiblywith fewer loops and more silicone bridges between hydrocarbon chains.

[0027] The texts of the above-cited U.S. Pat. Nos. 5,703,163, and5,811,193 are expressly incorporated herein by reference.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0028] The following Examples are presented to illustrate the invention.

EXAMPLES Materials

[0029] Toluene was dried over molecular sieves (3A,4-8 mesh).Polybutadiene (Mn 100,000, 93% vinyl olefin) was used as received fromScientific Polymer Products, Inc. Hydride-terminatedpoly(dimethylsiloxane) (Mn 400), ethoxy-terminatedpoly(dimethylsiloxane) (Mn 360-450), and dimethylethoxysilane wereobtained from United Chemical Technologies, Inc. Wilkinson's catalyst,tris(triphenylphosphine)rhodium(I) chloride, was purchased from AldrichChemical Co. FTIR spectra were recorded using a Perkin Elmer model 1605spectrometer.

Example I

[0030] Side-Loop Polymer Solution: PDMS-PBD-DMES

[0031] Hydride-terminated poly(dimethylsiloxane), (PDMS), andWilkinson's catalyst tris(triphenylphosphine)rhodium(I) chloride wereadded to a solution of polybutadiene (PBD) in toluene at 50-60° C. undernitrogen. The mixture was refluxed under nitrogen until IR analysis ofaliquots indicated the absence of Si—H absorption at 2125 and 909 cm⁻¹.The solution was cooled to 50-60° C., and dimethylethoxysilane (DMES)and additional catalyst were added. The solution was stirred at 105° C.until the infrared Si—H absorption at 2110 and 909 cm⁻¹ had disappeared.Examples are summarized in Table 1. TABLE 1 Hydrosilylation of PBD withPDMS and DMES^(a) Step 1 Step 2 PDMS^(c) PBD^(d) Cat^(e) Time^(f) DMESCat^(e) Time^(g) Adduct^(b) wt(g) eq SiH wt(g) eq vinyl wt(mg) hr wt(g)eq SiH wt(mg) hr H1V2D0.1 6.32 0.0316 3.68 0.0632 25 90 0.33 0.0032 3.568 H1V3D0.5 5.35 0.0268 4.67 0.0802 21 25 1.39 0.0133 4.7 112 H1V5D0.84.08 0.0204 5.93 0.1019 17 22 1.77 0.0170 5.0 93

Example II

[0032] Polybutadiene Dimethylethoxysilane Adduct Solution: DMES-PBD

[0033] Dimethylethoxysilane and Wilkinson's catalysttris(triphenylphosphine)rhodium(I) chloride were added to a solution ofpolybutadiene in toluene at 50-60° C. under nitrogen. The mixture wasstirred at 105° C. under nitrogen until IR analysis of aliquotsindicated the absence of Si—H absorption at 2110 and 909 cm⁻¹. TABLE 2Hydrosilylation of PBD with DMES² DMES PBD^(b) Cat^(c) Time^(d) Adductwt(g) eq SiH wt(g) eq vinyl wt(mg) hr 1:2 DMES-PBD 4.73 0,0454 5.270.0906 23 113 1:3 DMES-PBD 3.73 0.0358 6.25 0.1075 18 41 1:5 DMES-PBD2.64 0.0253 7.36 0.1265 14 46

Example III

[0034] Preparation of Coating Solutions

[0035] Formulations were prepared as shown in Table 3. An appropriatealiquot of the PDMS-PBD-DMES solution was concentrated in vacuo to leavea 45-50 wt % polymer solution. Dimethylethoxy-terminated PDMS and asolution of dibutyltin diacetate catalyst were added. The mixture wasreconcentrated to approximately 45 wt % PDMS-PBD-DMES. Trifluoroaceticacid catalyst was then added and the solution was applied substrateimmediately.

[0036] For DMES-PBD, an aliquot of the toluene solution was concentratedin vacuo to a 25-30 wt %. After dimethylethoxy terminated PDMS and thetin catalyst solution were added, the solution was reconcentrated toabout 25 wt % DMES-PBD. Trifluoroacetic acid was diluted with a smallamount of toluene and added. The solution was used immediately. TABLE 3Weight % of individual ingredient per total wt of all ingredients.PDMS-PBD- side DMES or EtO- total Polymer loops DMES-PBD^(a) PDMS^(b)DBTDA^(c) TFA^(d) PDMS 1 1:2:0.1 y 96.81 1.69 0.47 0.94 64.17PDMS-PBD-DMES 2 1:3:0.5 y 93.29 5.40 0.41 0.82 60.55 PDMS-PBD-DMES 31:5:0.84 y 82.49 16.67 0.42 0.35 57.63 PDMS-PBD-DMES 4 1:2 DMES-PBD n57.74 41.92 0.29 0 69.17 5 1:3 DMES-PBD n 63.37 36.25 0.32 0 59.95 6 1:5DMES-PBD n 70.82 28.75 0.35 0 47.45 7 1:2 DMES-PBD n 57.47 41.72 0.290.51 68.90 8 1:3 DMES-PBD n 63.13 36.11 0.32 0.42 59.72 9 1:5 DMES-PED n70.52 28.63 0.35 0.49 47.25

[0037] The rigidity of the samples listed in Table 3 upon curing isrelated to the degree of crosslinking, which is related to the amount ofDMES in the formulation.

Example IV

[0038] Storage life of 1:3 DMES-PBD with and without ethoxy-terminatedPDMS or dibutyltin diacetate was investigated. The results indicatedthat the presence of ethoxy-terminated PDMS had only a small effect onthe storability of the solution, but storage life was shortened moresignificantly by adding dibutyltin diacetate. The crosslinking reactionis accelerated by trifluoroacetic acid. These components can be combinedjust prior to use as a 2-part system. A 40% solution of 1:3:0.5PDMS-PBD-DMES can be stored for more than 3 months. A two-part RTVsystem can include DMES-PBD (25-30 wt %) or PDMS-PBD-DMES (45-50 wt %)in toluene as part A and a mixture of ethoxy-terminated PDMS, dibutyltindiacetate, and trifluoroacetic acid as part B. An alternative is toexclude ethoxy-terminated PDMS from part B and add it into part A forstorage. When parts A and B were mixed after storage for 3 weeks, clear,strong films were obtained when ethoxy-terminated PDMS was included inpart A, but weak hazy films were obtained when this component wasincluded in part B. TABLE 4 Storage life. Formulation Storage life(days) 1 27.65% 1:3 DMES-PBD >90 72.35% Toluene 2 27.09% 1:3DMES-PBD >60 12.71% Ethoxy-terminated PDMS 60.20% Toluene 3 28.79% 1:3DMES-PBD 20 13.61% Ethoxy-cerminated PDMS  0.11% Dibutyltin diacetate57.49% Toluene

[0039] Cure and Properties

[0040] Cure was effected by exposure to atmospheric moisture at roomtemperature. The cure rate depends upon the humidity of atmosphere andthe thickness of the coating. Optionally, acidic cocatalysts may beused. For example, tack-free time was dramatically reduced by the use oftrifluoroacetic acid. After mixing with the acid, the sample must beused immediately.

[0041] The films cast from these silicone compositions when cured arevery strong, and optically clear. Coating substrates may be plastics,metals or glass, and good adhesion was obtained without the use ofprimers.

1. A substrate having an adherent coating thereon which is a moisturecured polymer composition comprising (a) a member selected from thegroup consisting of a polydiolefin polymer containing olefinicunsaturation in either the main polymer backbone or in pendent sidechains; and (b) a silicon cross-linking compound containing at least oneeasily hydrolyzed substituent and at least one hydride substituent. 2.The substrate of claim 31 wherein cross-linking occurs about roomtemperature.
 3. The substrate of claim 31 wherein the cross-linkingoccurs at a temperature of about 0° F. to 100° F.
 4. The substrate ofclaim 31 wherein the substrate is a ship hull.
 5. The substrate of claim31 wherein the polydiolefin has a molecular weight up to about 100,000.